Various chemical thermal packs have been proposed heretofore which contain a suitable liquid solvent, principally water, and a quantity of particulate material that absorbs heat or produces heat when dissolved in that liquid. These ingredients may be packaged in a flexible sealed pouch, with the liquid solvent segregated from the powder by a membrane that ruptures when the pouch is manually squeezed. When the solvent and powder mix with each other, the powder either produces heat or absorbs heat, depending upon its composition.
One example of a heat-producing thermal pack is disclosed in U.S. Pat. No. 3,328,136, as including a suitable heat-producing particulate material having magnesium sulfate as its principal constituent. The liquid solvent for such heat-producing particulate material preferably is at least 90% water, with a few drops of coloring and the remainder is an organic salt, such as sodium chloride or potassium chloride, to give the liquid solvent a lower freezing point. Alternatively, the hot pack may have calcium chloride as the principal ingredient of the heat-producing powder and water as the solvent.
As an example of a heat-absorbing thermal pack, a suitable heat-absorbing particulate material, as disclosed in U.S. Pat. No. 2,979,463, may have as its principal ingredient urea or a urea compound, as a temperature depressant, along with the following:
One or more additional temperature depressants, such as ammonium chloride, potassium chloride or sodium chloride;
One or more heat-insulating substances, such as plaster of Paris or asbestos, to prolong the refrigerating effect;
One or more water absorbers, such as locust bean gum, and other minor constituents.
The liquid solvent for such heat-absorbing particulate material preferably is water with a few drops of coloring.
Alternatively, the cold pack may have ammonium nitrate as the principal ingredient of the heat-absorbing powder and water as the solvent.
A third type of thermal pack, known as a gel pack, can be placed in a hot or cold environment and will stay at a particular temperature when removed from that environment. Such a pack may contain water mixed with urea, potassium chloride and a gum such as locust bean gum. Alternatively, a water solution of calcium chloride may be used as the heat- or cold-sustaining mixture.
Such thermal packs have various uses, such as to warm the hands, or warm a baby bottle. The packs may also be used to warm, or cool an injured or painful part of the body, and in a great number of other situations that arise where promptly available, localizing heating or cooling effect for a limited period of time is desired.
Many such previous thermal packs were not entirely satisfactory from the standpoints of thermal efficiency and convenience of use because the heat transfer action takes place relatively freely at all exposed surfaces of the pack, with a resulting waste of the heating or cooling effect and often personal discomfort to the person holding the pack.
To overcome these deficiencies, it has been proposed heretofore to attach single-layer or multi-layer heat insulation to the outside o the inside of thermal packs. The arrangement with the insulation attached on the outside enables the interior of the thermal pack to be constructed substantially as before, but this tends to complicate and increase the cost of manufacture of thermal packs.
An example of a thermal pack with the insulation on the inside is U.S. Pat. No. 3,874,504. This patent is directed to a chemical thermal pack which has a sealed intermediate envelope filled with the powder that produces or absorbs heat when dissolved in water and a quantity of water separated from the powder by a membrane that may be readily ruptured. A relatively flat, sealed, flexible outer pouch slidably receives the filled intermediate envelope and the heat insulation sheet that is located along the inside of one major face of the pouch to retard heat transfer there when the pouch is squeezed manually to rupture the membrane. The patent also discloses use of an insulated pack containing gel in place of the powder and water.
Although this pack has met with great success, there is still room for improvement especially as it relates to the more economical production of a chemical thermal pack as well as a pack with increased durability and simplicity of construction.
The present invention is directed toward filling those needs.